Method of manufacturing electric lamps or similar devices



July 19, 1960 R. N. MALM EI'AL 2,945,327

METHOD OF MANUFACTURING auac'rmc LAMPS 0R SIMILAR mavrcss Original FiledNov. 28. 1955 lnvervtor'sz RObTt' M. MaLm, Vincervt Vodicka;

b9 l eir r ii eg. I:

2,945,327 Patented July 19, 1960 METHOD F MANUFACTURING ELECTRIC LAMPSOR SHWILAR DEVICES Original application Nov. 28, 1955, Ser. No. 549,424,

now Patent No. 2,904,716, dated Sept. 15, 1959.. Di- .vided and thisapplication May 8, 1957, Ser. No.

57,774 4 Claims. 01. '4978) Our invention relates to electric lamps orsimilar devices and to a method of manufacture thereof. The invention isof particular utility in connection with the manufacture of electriclamps of the type having an external stem press through which thelead-in wires of the lamp are sealed. The present application is adivision of our co-pending application Serial No. 549,424, filedNovember 28, 1955, which issued as Patent No. 2,904,716, dated September15, 1959 and is assigned to the assignee of the present invention.

Electric lamps and other similar type devices commonly consist of anenclosing envelope or bulb having a glass stem press portion throughwhich the lead-in Wires of the lamp extend and are sealed. These glassstem press portions are usually provided with an exhaust passagewayextending therethrough which communicates with the interior of theenvelope and through which the envelope is subsequently exhausted and,if desired, filled with a suitable inert gas at a suitable pressure.

The glass press portions are generally formed by the fusion of a glassexhaust tube to a surrounding tubular glass body such as a stem tube orthe tubular neck portion of a lamp bulb. The lead-in wires arepositioned and held in place between the two glass tubes, during theinterfusion thereof, and the heated and softened glass is compressed bythe closure of opposed jaws thereagainst to form a press portion throughwhich the leadin wires extend and are hermetically sealed. Thiscompression of the softened glass tubes, however, to form the stem pressnormally results in the closureof the passageway through the exhausttube, a condition which of course would prevent subsequent evacuation ofthe lamp envelope or bulb. For such reason it is necessary, during thepress-forming operation, to adopt additional procedures or steps whichwill insure the provision of an exhaust passageway through the completedstem press. In the usual case where the stem press is located internallyof the lamp envelope or bulb, the exhaust passageway through the stempress is customarily produced by blowing a hole through the side of thepressed portion while the glass thereof is still in a heated and plasticstate, the blow-out being accomplished by the force of a blast ofcompressed air introduced into the open outer end of the exhaust tube.disclosed in Mitchell and White Patent 1,423,956 and is the standardprocedure employed in the manufacture of conventional type incandescentlamps having internal stem presses. However, such a procedure cannot beemployed where the stem press is located externally of the bulb as, forexample, in the case of the miniature bi-pin incandescent lamp recentlyintroduced on the.

market by applicants assignee and commerciallydesignated as their No. 10lamps. In suchcase, a side-opening exhaust passageway through the stempress would open to the outside atmosphere only, instead-of into theinterior of the lamp envelope or bulb. As a result, there would be noexhaust passageway through the stem press This is the method which isleading into the interior of the envelope through which the envelopecould then be exhausted.

For such reason, other procedures have been proposed and followed, inthe case of lamps having external stem presses, to insure the provisionof an exhaust passageway through the stem press communicating with theinterior of the lamp envelope. Heretofore, such procedures havegenerally involved either the insertion of metal sleeves, springs orother similar liners in the exhaust tube, or the temporary introductionof a mandrel into the exhaust tube during the press-forming operation,for the purpose of maintaining the opening through the exhaust tube.However, these prior procedures for various reasons have not beenentirely satisfactory. The

use of metal sleeves or bushings, for instance, in the exhaust tube,besides being rather expensive, also introduces strains in the glassstem press which frequently results in the cracking of the press, thuscausing an undesirably high percentage of manufacturing rejects orso-called shrinkage. Likewise, the temporary insertion of a mandrel intothe exhaust tube during the pressforming operation frequently results inthe sticking of the plastic glass to the mandrel and consequent breakageof the glass press when the mandrel is subsequently withdrawn from theexhaut tube. It has also been pro-. posed, in the manufacture of vacuumor radio tubes, to employ a liner for the inner wall of the exhaust tubein the form of a graphite coating thereon. Such a material, however, iswholly unsuitable for use in tungsten filament incandescent lampsbecause of its deleterious effect on the lamp, the graphite reactingwith the tungsten of the filament at the incandescent operatingtemperature thereof and causing embrittlement of the tungsten filamentsuch as results in greatly foreshortened lamp life.

It is an object of our invention, therefore, to provide a novel methodof forming the'glass stem press of an electrical device having anexhaust passageway extending therethrough.

Another object of our invention is to provide a novel method of sealingand compressing a tubular glass member around an inserted glass exhausttube while preserving the opening therethrough to serve as an exhaustpassageway.

Still another object of our invention is to provide a novel andinexpensive method of manufacturing an electric incandescent lamp orsimilar device having a stem press with an exhaust passagewaytherethrough.

Briefly stated, in accordance with one aspect of our invention, anelectric incandescent lamp or similar device is constructed with a glassstem press having an exhaust passageway extending therethrough andmaintained open, during the press-forming operation, by a coating on thewall of the exhaust passageway of a material having a melting pointabove that of the glass and chemically inert with respect to thefilament at the incandescent operating temperature thereof. According toa further aspect of the invention, the coating material employed for'theabove mentioned purpose is one which, under theconventionalhigh-frequency glow test to which vacuum type electricincandescent lamps-or similar devices are subjected in order to indicatethe degree of vacuum in the device, will produce a bright and highlyconcentrated glow or spot of light'such as enables the ready and easydetection thereof and determination of the character of the vacuum inthe device by the test operator.

- Further objects and advantages of our invention will appear from thefollowing detailed description of species thereof and from theaccompanying drawing,

I lathe drawing, Fig. 1 is an elevational view partly in section showingthe component parts employed in the manufacture of an electricincandescent lamp according to the invention, the component parts beingshown in assembled position in readiness for sealing the lamp mount intothe lamp bulb and forming the glass stem press portion thereof.

Fig. 2 is a sectional view similar. to Fig. 1 and showingthe compressionof the bulb neck to form the stem press of the lamp;

Fig. 3 is a sectional view on the line 3-3 of Fig. 2, and

Fig. 4 is an elevation, partly in section, of a completed electricincandescent lamp comprising our invention.

Referring to the drawing, the invention is there shown as embodied in anelectric incandescent lamp of the type having an external stem press,such as the miniature bipin lamp recently introduced on the market byapplicants assignee and known as theirNo. 10 lamp. It should beunderstood, however, that the invention is applicable as well to othertypes of electric incandescent lamps and similar devices such as thosehaving re-entrant stems provided with stem press portions located withinthe envelope of the device.

As shown in Fig. 4, the particular electric incandescent lamp thereillustrated comprises a sealed glass bulb or envelope 1 provided with anoutwardly protruding pinched seal or press portion 2 through which aplurality (two in the particular case shown) of lead-in conductors -3, 3are sealed so as to extend parallel to each other in side-by-siderelation. The lead-in conductors 3, 3 are of the multi-section pin typesuch as are commonly employed in miniature radio tubes and comprisingrigid metal outer pin portions 4 and inner lead portions 5 which arehermetically sealed in the envelopepress 2, the two sections 4 and 5 ofeach conductor being butt-welded together in end-to-end relation. Theouter pin portions 4 may be made, for example, of nickel wire having adiameter for instance of V inch. The inner lead'portions 5 may be madeof conventional Dumet wire com monly employed in the lamp making art forsealing into glass. The metal outer pins 4 serve as terminal contactsfor the lamp and for such purpose are embedded at their inner ends inthe glass of the press 2 in order to firmly anchor or support the pinsin place from the press. The inner leads 5 are connected to anelectrical energy translation element such as a filament 6 comprised,for example, of a wire of tungsten or other suitable refractory metal incoiled or coiled-coil or any other suitable form. The envelope 1 isevacuated to the degree customary for conventional vacuum typeincandescent lamps. The press portion 2 of the lamp envelope 1 isprovided with an exhaust passageway 7 which extends through the press 2at a point between the two conductors 3, 3 and which serves as a meansfor evacuating the lamp envelope 1.

In accordance with the invention, the exhaust passageway 7 isconstituted by the bore 8 of a glass exhaust tube 9 which is sealedinithe stem press 2 and the bore of which is maintained open during thepress-forming operation. To this end, the end portion of the exhausttube which is fusion-sealed into the stem press 2 is provided with afirmly adherent coating 10 of a suitable inorganic material which has amelting point above that of the glass of which the stem press isconstituted and which is chemically inert with respect to the lampfilament 6 at the incandescent operating temperature thereof, the saidmaterial acting to raise the melting point of the glass underlying thecoating during the press-forming operation. Alternatively, the coating10 may be of a material which, when subjected to the heat attending thepress-forming operation, will be transformed into an inorganic materialhaving the above-stated properties. Since the glass lamp parts (i.e.,the exhaust tube and the bulb or stem tube) from which the stem pressesof electric lamps are fabricated, are customarily made of so-called softype glasses having a melting point of around 650 C., the coatingmaterial 10 in such case should be one having a melting point above 650C. The coating material 10 should also be one which is both physicallyand chemically stable at temperatures up to at least the temperature(for example at least 700 C.) which the glas ex,

haust tube 9 will attain during the tipping-0d thereof, otherwisecontamination of lamps will occur from the gases or other contaminatingimpurities introduced in the lamp envelope by unstable coatingmaterials. While the coating 10 is preferably applied-on the internalwall of the exhaust tube 9 as shown, it may be applied instead on theexternal. wall thereof as shown in dotted lines at 10 in Fig. 1 or itmay be applied on both the inside and outside walls of-the exhaust tube.The coating 10 or 10 is applied to the exhaust tube 9 prior to thepressforming operation. During the heating and interfusion of the end ofthe exhaust tube 9 and the surrounding neck 11 of the' lamp bulb 1 toform the stem press 2, the coating 10 on the exhaust tube acts tomaintain the bore of the exhaust tube open so as to leave an exhaustpassageway 7 through the stem press. While the exact manner in which thecoating 10 acts to accomplish this object is not known, it is believedthat the coating acts either to raise the melting point of the glass ofthe exhaust tube so that it is at a temperature below that at which itis appreciably plastic, or to raise the surface tension of the glass sothat the coated surfaces of the exhaust tube do not wet together andclose oif the bore of the exhaust tube.

There are a number of materials which may he satisfactorily employed ascoating materials 10 for the purposes of the invention. Thus, thecoating 10 on the exhaust tube 9 may consist of aluminum or silver, orthe oxides of aluminum, silver, zirconium, magnesium, titanium, zinc,tin, calcium, barium, and strontium, or refractory materials such assilicates, double silicates and titanates. It is' preferable to employcoating materials 10 such as those specified above which are light orwhite in color not only because of their better appearance and the easeof discerning whether lamp-contaminating impurities are present in thecoating 10 but primarily because of the greater heat-reflectivitycharacteristic of such light-colored coatings 10 which thereforeminimizes or lessens the softening and likelihood of closing of theglass exhaust tube during the press-forming operation. As a result,considerably greater latitude in the degree of heating of the glassparts, during the press-forming operation, is afiorded by the use ofsuch light or white-colored coatings 10, as compared to dark coloredcoatings, without encountering closure of the exhaust tube. This meansthat considerably greater freedom is permitted in the setting of the gasfires which are ordinarily used to melt and fuse the glass parts. Thiscomparatively wide range of permissible gas fire settings thereforerenders the stem press making process according to the inventioncommercially practical for'high speed production manufacture since itresults in -a very low percentage (2% or less) of production rejects dueto closed exhaust tubes.

Of the various coating materials 10which have been found satisfactoryforthe purposes of the invention, the oxide and silicates (both singleand double) of zirconium are preferred for the reason that they performthe additional function of producing a bright and distinctive coloredglow Within the lamp envelope 1 during the customary high-frequency glowtesting of the lamp for the determination of the degree of vacuum in thelamp envelope. This glow of light, which appears as a green column oflight withinthe exhaust passageway 7, is of particular utility in thecase of lamps having envelopes or bulbs 1 of low light transmissivitysuch as where the bulbs are provided with enamel or other coatings. Insuch case, the color of the glow discharge ordinarily is not discerniblein the absence of zirconium oxide or zirconium silicate coating materialwithin the exhaust passageway 7. However, because of its brightness, thegreen glow of light produced by a zirconium oxide or zirconium silicatecoating 10 within the exhaust passageway 7, dur ing the high-frequencyglow testing of the lamp, still can be observed through a lamp bulb oflow light transmissiyity. Moreover, even in the case of devices havingbulbs which are completely opaque except for a protruding external stempress, the bright green glow of light produced within the exhaustpassageway 7 of the stem press by a zirconium oxide or silicate coatingtherein, during high-frequency glow testing of the device, neverthelessis still readily observable through the protruding stern press. Of thezirconium-containing glow-producing materials which are suitable ascoating materials 10, however, zirconium oxide is preferred because itproduces the brightest light glow on high-frequency glow testing of thelamp. I

From the standpoint of their relative effectiveness in maintaining theexhaust tube open during the press-formirig operation, magnesium oxideand the oxide and silicates of zirconium have been found to be the mosteffective for such purpose. Thus, the use of such materials as thecoating 10 on the exhaust tube 9 in the production manufacture ofincandescent lamps has been found to produce less than /2 percent ofproduction rejects due to closed exhaust tubes 9.

Where the coating 10 on the exhaust tube 9 consists of an oxide or arefractory material, it is preferably applied thereto as a powdercoating. The powdered material is suspended in a suitable vehicle toform a slurry of suitable viscosity which, for the application of acoating to the inside wall of the exhaust tube, is drawn into theexhaust tube the desired distance from the end thereof and then allowedto flow out of the exhaust tube so as to deposit a coating of the slurryon the inside wall of the exhaust tube. The vehicle employed forsuspending the powdered coating material may be of any suitablecharacter. For example, where the coating material consists of magnesiumoxide, the suspending vehicle may consist of a suitable denaturedalcohol such as that commercially known as Synosol. The proportion ofmagnesium oxide to alcohol is not critical. Thus, 100 to 250 grams ofmagnesium oxide per 1000 ml. of alcohol will give satisfactory coatings.To reduce and delay the thickening of this slurry, a small amount ofacetic acid may be added to the suspension in the range of, for example,a few drops to one or two ml. per 100 ml. of suspension. Furtherimprovement in this respect is obtained by the addition of a smallamount of a suitable sequestering agent such as ethylene diaminetetraacetic acid (commonly known as EDTA) for sequestering the free ionspresent in the suspension and rendering them inactive. Thus, an additionof from /2 to 1 ml. of a 5% solution of ammonium salt of EDTA to 100 ml.of the suspension has been found satisfactory for this purpose. Toimprove the adherence of the powdered magnesium oxide coating to thewall of the exhaust tube, and at the same time improve .the uniformityof the coatings on the exhaust tubes, at small amount of a suitablebinding agent such as ethyl borate may also be added to the suspension.Thus, from 1 to 5 ml. of ethyl borate per 100 ml. of the magnesium oxidesuspension will alford the above mentioned improvement.

Where the coating material. 10 consists of zirconium oxide, thesuspending vehicle used to form the zirconium oxide suspensionpreferably comprises water and a small addition of a suitable bindersuch as polymerized (i.e., a. copolymer of) vinyl methyl ether andmaleic anhydride, commonly known as PVM/MA. While other vehicles may beused for suspending powdered zirconium oxide, water is advantageous forsuch purpose because of its non-explosive and non-toxic character andits relative inexpensiveness. The polymerized vinyl methyl ether andmaleic anhydride is used to increase the viscosity of the zirconiumoxide slurry, to improve the suspension of the zirconium oxide particles(it acts partially as a dispersing agent), and to give good andconsistent coatings on the exhaust tubes. Preferably, in addition, smallamounts of ammonium hydroxide and boric oxide are also incorporated inthe zirconium oxide slurry. The ammonium hydroxide addition is employedto control the pH of the slurry and thus control its viscosity. Theboric oxide addition to the suspension is employed as a fusing orsintering agent to obtain improved adherence of the zirconium oxidepowder particles to the wall of the exhaust tube after the binder isburned off. Without boric oxide in the zirconium oxide coating slurry,the zirconium oxide tends to flake off the wall of the exhaustpassageway 7 in the press 2 of the finished lamp. While loose zirconiumoxide powder in the lamp envelope 1 is not detrimental to lamp quality,nevertheless the presence of such loose powder within the lamp envelopeis more or less undesirable from an appearance standpoint.

The application of the coating of slurry to the wall of the exhaust tube9 is preferably accomplished by positioningthe end of the exhaust tubeto be coated so as to touch the surface of asupply of the coatingslurry. Capil lary action then draws the slurry up into the exhausttube.

The height to which the column of slurry rises in the exhaust tubeordinarily is quite variable. However, by adding a small amount of ethylborate to the slurry, for example, 10 ml. of ethyl borate per 300 gramsof slurry, the height of the slurry rise in the exhaust tubes becomesmuch more uniform.

As a specific example, a suitable zirconium oxide slurry for applicationto the walls of exhaust tubes 9 may be prepared by milling for anextended period, preferably from 24 to 48 hours or so, a mixture of thefollowing general composition;

Zirconium oxide grams '1200 Water ml 800 Polymerized vinyl methyl etherand maleic anhydride (10%) ml 40 Ammonium hydroxide ml 40 Boric oxide ml18 After milling of the above ingredients, the milled suspension iswashed out of the milling container with 400 ml. of water containing 4ml. of a suitable wetting agent such as that commercially known asIgepal 530, which is a polyoxyethylated nonylphenol of such ethyleneoxide nonylphenol balance as to give medium hydro! phobic qualities. Itis a surface-modifying agent used to give coatings free of pin holes andother coating defects. The resulting milled zirconium oxide slurry hasexcellent keeping properties. For example, even after an extended periodof three months or so it does not exhibit any deterioration or gelling.Shortly before use of this zirconium oxide slurry to coat exhaust tubes(preferably not more than 112 hours or so before use), 10 ml. of ethylborate is added to each 300 grams of the slurry. This ethyl borateaddition improves the coating characteristics of the slurry when appliedto the exhaust tubes. Inasmuch as the keeping quality of the coatingslurry after the addition of ethyl borate is relatively poor, the slurrywith the ethyl borate addition should be used within a relatively shortperiod of not more than 24 hours or so.

After the application of the slurry coating to the wall of the exhausttube 9, the latter is then heated to a temperature sufficiently high,and for a period of time longenough to dry, and burn out the binder inthe coating on the exhaust tube and to partially sinter or bind thepowder particles of the coating onto the wall of the exhaust tube. Tothis end, the exhaust tube is heated to a temperature just below thepoint at which it will soften and distort. For example, in the case ofthe soft lead or lime glasses which are ordinarily used for exhausttubes and having a melting point of around 650 C., the exhaust tubeshould be heated to a temperature of the order of 600 to 650 C. at whichtemperature the binder will be burned out of the slurry coating on theexhaust tube and the powder particles of the coating will,

be set onto the wall of the tube. A uniform and firmly adherent powdercoating is thereby produced on the wall of the exhaust tube which willnot flake off during the handling of the exhaust tube and during theformation of the-stem press and after the lamp has been completed.

In the manufacture of the lamp or other device according totheinvention, a glass exhaust tube 9 having a coating 10 thereon, a mountstructure 12 and a glass envelope or bulb 1 are first positioned inproper sealing relation to each other (as illustrated in Fig. 1) in oneof the sealing heads (not shown) of a conventional type lamp sealing-inmachine such as commonly employed in the lamp-making art. As shown, themount 12 comprises a pair of leadin conductors 3 and the filament 6which is connected at its ends across the tips of the inner leadportions 5 of the lead-in conductors 3. The bulb'l is supported with itsneck end 11 down, and the mount 12 is supported in a vertical positionwith the heavy end or pin portions 4 of the conductors 3 down andextending part way into the bulb neck 11 and with the filament 6 locatedwithin the bulbous portion of the bulb. The glass exhaust tube 9 issupported in a vertically extending position with its coated end 13uppermost and located within the bulb neck 11 in a position between thetwo conductors 3.

With the exhaust tube 9, mount 12 and bulb 1 thus supported in place inthe sealing head of the sealing machine in position for sealing, theneck 11 of the bulb is suitably heated as by gas fires 14 directedagainst opposite sides of the bulb neck, as shown in Fig. 1. Uponsoftening of the glass of the bulb neck,it gathers together andcontracts against the upper coated end 13 of the exhaust tube 9 which istherefore heated and softened by radiation and conduction of heat fromthe hot glass of the bulb neck. The heating of the bulb neck 11 by thegas fires is so controlled as to maintain the temperature of the coatedend of the exhaust tube below the temperature at which it becomesappreciably plastic, the coating lfl on the exhaust tube assisting inmaintaining this temperature control. The heating is continued until thesoftened glass of the bulb neck 11 and exhaust tube 9 becomes thoroughlyinterfused, whereupon the gas fires 14 are removed and, as shown inFigs. 2 and 3, the molten glass of the bulb neck then pinched, as bymeans of pinching jaws 15 to press the glass completely around the innerlead portions 5 of the conductors 3 as well as around the inner or upperend portions of the pin ends 4 of the conductors 3 and into intimatecontact with the glass of the exhaust tube so as to form a solid mass ofglass embedding the conductors 3 and constituting a press 2.

During the fusion operation, as well as the subsequent pinchingoperation, the coating on the wall of the exhaust tube 9 effectivelyprevents collapsing of the exhaust tube within the press 2 and resultantclosing of the bore 8 of the exhaust tube. However, to fully insureagainst closure of the bore 8 through the exhaust tube 9 by the pressureof the pinching jaws during the pinching operation, the pinching faces16 of the said jaws are suitably relieved as by being provided withvertically extending semi-cylindrical shaped recesses 17 which, when thejaws are in their fully closed position, are more or less concentricwith the exhaust tube 9, as shown in Fig. 3, and leave correspondingsemi-cylindrical shaped enlargements 18 in the completed press 2 on eachof its opposite sides. Y n a -After the pinching of themolten glass ofthe bulb neck 11 and exhaust tube 9 to form the press 2 of the lamp, thepinching jaws 15 are removed or opened and gas fires then directed oncemore against the pressed glass 2 first to further interfuse and work theglass thereof and then to anneal the glass so as to remove any strainsdeveloped therein during the pinching operation, the coating 10 on thewall of the exhaust passageway 7 meanwhile continuing to perform itsfunction of maintaining the exhaust passageway open through the stempress 2. g

Upon completion of the sealing operation as above described, the lampenvelope 1 is evacuated to the desired degree of vacuum through theexhaust tube 9 and through the exhaust passageway 7 in the stern press"2; after which the projecting exhaust tube is then tipped off as.closely as possible to, and preferably at the very junction with thepress 2, as shown at 19 in Fig; 4, to thereby hermetically seal the lampenvelope. The tipping-off of the exhaust tube 9 may be accomplished inthe conventional manner by directingsharp gas fires against oppositesides of the'exhaust tube at a point immediately adjacent the stem press2,'the glass wall of the exhaust tube collapsing upon softening andforming a tip 19 closing off the exhaust passageway 7. Because of thephysically and chemically stable character of the coating material 10within the exhaust tube at'the temperature to which it is subjectedduring this tippingoif operation, no contaminating impurities are formedby the coating material and introduced into the lamp envelope 1 duringthe tipping-off operation such as to cause contamination of the lamp andadversely affect the operation thereof.

Although a preferred embodiment of our invention has been disclosed itwill be understood that the invention is not to be limited to thespecific construction and arrangement of parts shown, or to the specificprocedures described, but that they may be widely modified within thespirit and scope of our invention as defined by the appended claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In the manufactureof anelectrical device, the method of sealing anend portion of a glass exhaust tube into a surrounding glass memberwhich comprises applying to the inner wall of the said end portion ofthe exhaust tube a coating of an inorganic material of the groupconsisting of magnesium oxide and the oxide and silicates of zirconium,heating the surrounding glass member and the inserted coated end portionof the exhaust tube to a temperature sufficient to soften and fuse themtogether and at which the said coating will react with the underlyinginner wall surface of the glass tube to raise the softening pointthereof to a degree effective to prevent collapsing of the glass tubeand closure of the passageway. therethrough at the saidtemperature, andthen pinching the softened glass of the said glass member to form itinto a press portion and compress it around the exhaust tubesufiiciently to firmly unite therewith but insufficiently to close thepassageway through the said exhaust tube. 5

2. In the manufacture of an electrical device, the method of sealing anend portion of a glass exhaust tube into a surrounding glass-memberwhich comprises applying to the inner wall of thesaid end portion of theexhaust tube a coating of powdered zirconium oxide, heating thesurrounding glass member and the inserted coated end portion of theexhaust tube to a temperature sufficient to soften and fuse themtogether and at which the said coating will react with the underlyinginner wall surface of the glass tube to raise the softening pointthereof to a degree effective to prevent collapsing of the. glass tubeand closure of the passageway therethrough at the said temperature, andthen pinching the softened glass of the said glass member to form itinto a press portion and compress it around the exhaust tubesufficiently to firmly unite therewith but insufficiently to close thepassageway through the said exhaust tube.

.3. In the manufacture of an electrical device, the method of sealing anend portion of a glass exhaust tube into a surrounding glass memberwhich comprises applying to the inner wall of the said end portion ofthe exhaust tube a coating of a suspension comprising a powderedmaterial of the group consisting of the oxides of zirconium andmagnesium suspended in a suitable vehicle and containing a binder,heating the coated exhaust tube to the softening temperature thereof todry the coating and burn out the binder therein and set the powderedmaterial thereof onto the wall of the exhaust tube, positioning thecoated end of the exhaust tube within the glass member, heating the saidglass member and the inserted coated end portion of the exhaust tube toa temperature sufiicient to soften and fuse them together and at whichthe said coating will react with the underlying inner wall surface ofthe glass tube to raise the softening point thereof to a degreeeffective to prevent collapsing of the glass tube and closure of thepassageway therethrough at the said temperature, and then pinching thesoftened glass of the said glass member to form it into a press portionand compress it around the exhaust tube sufficiently to firmly unitetherewith but insufiiciently to close the passageway through the saidexhaust tube.

4. In the manufacture of an electrical device, the method of sealing anend portion of a glass exhaust tube into a surrounding glass memberwhich comprises applying to the inner wall of the said end portion ofthe exhaust tube a coating of a suspension comprising powdered zirconiumoxide suspended in water and containing small amounts of boric oxide,ammonium hydroxide, ethyl borate and a copolymer of vinyl methyl etherand maleic anhydride, heating the coated exhaust tube to the softeningtemperature thereof to dry the coating and burn out the binder thereinand set the powdered material thereof onto the Wall of the exhaust tube,positioning the coated end of the exhaust tube within the glass member,heating the said glass member and the inserted coated end portion of theexhaust tube to a temperature sufficient to soften and fuse themtogether and at which the said coating will react with the underlyinginner wall surface of the glass tube to raise the softening pointthereof to a degree efiective to prevent collapsing of the glass tubeand closure of the passageway therethrough at the said temperature, andthen pinching the softened glass of the said glass member to form itinto a press portion and compress it around the exhaust tubesufiiciently to firmly unite therewith but insufficiently to close thepassageway through the said exhaust tube.

References Cited in the file of this patent UNITED STATES PATENTS1,565,598 Sproesser Dec. 15, 1925 1,569,185 Higgins Jan. 12, 19262,020,729 Knoeppel Nov. 12, 1935 2,762,168 McCutchen Sept. 11, 1956

